A Depressing Loss of Vision

Abstract

Sensory experience during development can profoundly affect brain function. For instance, undergoing a period of visual deprivation in one eye shortly after birth leads to blindness in that eye because neurons in the visual cortex of the brain lose the ability to respond to stimuli (see News and Views by McAllister and Usrey). This loss does not result simply from reduced neuronal activity, but depends on residual activity from the deprived retina. The underlying mechanisms, however, remain unclear. Heynen et al. compared the effects of monocular deprivation (MD) of vision in rats to those of long-term depression (LTD), a use-dependent decrease in synaptic efficacy that has been studied extensively in vitro, and found that brief MD elicited the same functional and biochemical changes as LTD. Both LTD (produced by electrical stimulation in vivo) and MD diminished the electrical response of the visual cortex to a visual stimulus. MD in young rats produced changes in the phosphorylation status and cell-surface expression of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) that are characteristic of those seen with LTD. MD led to dephosphorylation of Ser 845 on the GluR1 subunit, no change in Ser 831 , increased phosphorylation of Ser 880 on the GluR2 subunit, and decreased AMPAR cell-surface expression. Like LTD, changes in AMPAR phosphorylation depended on N -methyl-D-aspartate receptor activation. Moreover, brain slices from rats that had undergone MD showed diminished capacity for LTD, as expected if the two processes depended on the same saturable mechanisms. The authors concluded that MD produces LTD and that LTD contributes to the loss of vision that follows MD. A. J. Heynen, B.-J. Yoon, C.-H. Liu, H. J. Chung, R. L. Huganir, M. F. Bear, Molecular mechanism for loss of visual cortical responsiveness following brief monocular deprivation. Nat. Neurosci . 6 , 854-862 (2003). [Online Journal] A. K. McAllister, W. M. Usrey, Depressed from deprivation? Look to the molecules ..., Nat. Neurosci. 6 , 787-788 (2003). [Online Journal]